I've seen 420s that run and some that don't. It depends on how well they are tuned. I am impressed with the way that my 420 runs, but it can't show its full potential draggin' because I don't run a longer swingarm. As a matter of fact, I run a completely stock chassis. Mine is a Trinity Stage III, 33 PWK's, and I've run 4.8's in 300ft (stock tranny also). I think that is pretty quick considering what it is.
In a 200ft drag, someone without as much power can beat you if they get off the line a lot better. Just like a turbo DS. Awesome power but gets beat because he can't keep the front end down. Besides, most drags run well in excess of 200ft.
I guess what I'm saying is that the 420s can run. But expect to put a longer swingarm on it, otherwise someone with a lengthened modified 350 can beat you.
Daren